This invention relates to mobile type cranes and more particularly to a steering system for mobile cranes which permits both two and four wheel steering modes.
Stradle type gantry cranes are commonly employed for lifting and moving large bulky objects, such as shipping containers, structural members, modular building sections, heavy machinery and equipment and the like. Such devices are well-known and generally include a pair of inverted U-shaped gantries each comprising cross beams spanning vertical columns supported at their lower ends on wheels or truck assemblies. The two gantries are interconnected by spaced side members and may include hoists supported from cross beams by means of a trolly. This permits the load to be elevated and traversed laterally.
Mobile type cranes must be sufficiently maneuverable for being positioned above the load prior to elevation and for transmitting the load from one location to another. When operating in a shop or storage area, for example, the crane will normally be required to move longitudinally up and down an aisle and in addition, laterally between aisles. This requires a relatively flexible steering assembly. While four wheel gantry steering systems are known in the prior art, such as that disclosed in U.S. Pat. No. 4,284,159, there is a need for a steering system which performs the steering function but is relatively simpler and less costly.